The growth of hygroscopic particles in the human upper airways will be investigated as a function of flow rate and particle tonicity. Aerodynamic diameter changes from nasal entrance to oropharynx will be measured for hypertonic, isotonic, and hypotonic particles, as well as solid NaCl particles. Comparisons of parenchymal deposition of hygroscopic and nonhygroscopic aerosols will be made in normal subjects and subjects with acute and chronic respiratory disease. The applicability of lung deposition models such as the Task Group Model for hygroscopic aerosols will be evaluated based on these experiments. The effect of bronchoconstriction and bronchodilation on parenchymal deposition will be studied.